There is an increasing demand for rectangular chip resistors with highly accurate resistance to eliminate adjustment for electronic circuits as the size of electronic equipment continues to shrink. In particular, since the allowance required for the resistance of rectangular chip resistors is in the range of .+-.0.5% to .+-.0.1%, the demand for rectangular chip resistors made of thin metal film resistance, in which precise resistance is achieved more easily, is overtaking demand for conventional rectangular chip resistors which are constituted of thick film resistance made of grazed material.
Furthermore, the demand for multiple chip resistors, which are packages of two or more rectangular chip resistors, is increasing as a result of the need to increase the mounting density of electronic components on circuit boards. In the field of multiple chip resistors, the demand for thin film multiple chip resistors with a thin metal resistance (hereafter referred to as "resistors") is also overtaking demand for conventional multiple chip resistors with thick film resistance.
A conventional method for manufacturing resistors is explained below with reference to FIG. 4.
First, a substrate 21 made of 96% aluminum is supplied (Process A). The substrate 21 has an a surface a horizontal division groove (slit) 22 and vertical division grooves (slit) 23 at constant intervals so as to configure two or more resistance elements. Through holes 24 are provided in the horizontal division groove 22. A thin film top electrode layer 25, typically of Au, is formed on the top face of the substrate 21 across the horizontal division grooves 22 and at both sides of the through holes 24 (Process B).
Then, a thin film bottom electrode layer (not illustrated), typically of Au, is formed on the bottom face of the substrate 21 at a position corresponding to the top electrode layer 25 (Process C).
A thin film resistance layer 26 typically of NiCr is formed over the entire top face of the substrate 21 (Process D).
The thin film resistance layer 26 is then etched using photolithography, so as to leave a portion of the thin film resistance layer 26 connected to the top electrode layer 25 to form a pattern of a resistance 27 (Process E).
The resistance is corrected, by means such as a YAG laser, to adjust the resistance 27 to a specified value (Process F).
A resin paste, made typically of epoxy resin, is printed to completely cover an adjusted resistance 28, and then cured to form a protective layer 29 (Process G).
The substrate 21 is then primarily cut along the horizontal division groove 22 (Process H). A thin film side electrode layer 31 made of Ni system is formed on a cut face of the primary divided substrate 30 by means such as sputtering (Process I). Here, the side electrode layer 31 is formed only on the cut face of the primary divided substrate 30. It is not necessary to form the side electrode layer 31 on a side face of the through hole 24, which separates adjacent electrodes. Accordingly, a resist is applied to the side face of the through holes 24 before forming the side electrode layer 31, and the resist is removed after sputtering a thin Ni film by means such as the lift-off method in order to form the side electrode layer 31 only on the cut face.
Next, the substrate, after the side electrode layer is formed, is cut along the vertical division grooves 23 (secondary division) to make substrate pieces (Process J).
Lastly, an electrode plating layer 33 is formed on the entire face of the top electrode layer 25, bottom electrode layer, and side electrode layer 31 of a substrate piece 32 (Process K).
In the process of applying resist to the through holes 24 in the prior art, however, the resist may not be fully applied to the side face of the through holes 24 due to deviations. As a result, electrode material may attach to a part of the side face of the through holes 24 when forming a side electrode layer 31, as shown in FIG. 5, creating an electrode material spill 38. This causes short circuits between electrodes or solder bridges during soldering.